[farazbabar]

Because I am excited that this idea got turned into a viable product. And what is wrong with sharing the excitement with my fellow nerds including the fact that I had this idea first? It is all about execution and kudos to stripe for taking this idea forward and turning into a viable product.

[lostcolony]

Then perhaps a comment along the lines of "This is really neat! I'm so glad to see someone else doing this; I originally patented something akin to it and then (never used it/did and here's the thing I built), and it's awesome to see continued development in this area".

As it is, it's not clear what your intent is (hence my question). You aren't congratulating them. You aren't expressing excitement. To your credit, you also aren't claiming they're infringing, though it begins to approach it.

[stevenhuang]

Gumroad had this since 2011, 5 years before you filed your patent.